Wet-cold exposure and hypothermia: thermal and metabolic responses
to prolonged exercise in rain.
Thompson, Robert L., and John S. Hayward.
Department of Biology, University of Victoria, Victoria, B.C.,
Canada V8W 2Y2
APStracts 3:0225A, 1996.
Simulated conditions of hiking in rain, wind, and cold, without
protective rainwear, were used to investigate wet-cold hypothermia in
18 male subjects. Thermal, metabolic and motor responses were
monitored during an attempted 5-h walk (5.1 km x h-1) at 5 degrees C,
with continuous exposure to rain (7.4 cm x h-1) and wind (8.0 x km h
-1) over the final 4 h. The majority of subjects (11) could not
complete the protocol due to intolerance of wet-cold conditions
during the last 2 h. Therefore, data from 5 subjects who completed
the protocol in rain and control conditions were used to describe the
general pattern of response. During the first hour of walking, core
temperature rose 1 degrees C to 38.1 degrees C. The subsequent 2 h of
rain caused substantial cold stress, indicated by a 40% increase in
heat production due to shivering, and significant loss of strength
and manual dexterity. However, core temperature only decreased to
37.1 degrees C, merely eliminating the initial exercise hyperthermia.
Over the last 2 h of rain, core temperature remained relatively
stable at 36.8 degrees C, decreasing slightly to 36.4 degrees C by 5
h. Two other subjects developed significant hypothermia (35 degrees
C). One demonstrated fatigue of shivering after 2.5 h of rain,
confirming the exhaustion hypothesis of wet-cold hypothermia. The
other cooled rapidly when he failed to maintain the walking pace. We
conclude that if a person can tolerate the intense discomfort of
prolonged wet-cold exposure, he or she has the potential to resist
significant core hypothermia for at least 4 h of walking under the
conditions of this experiment. Exceptions to this generalization
occur, making exposure of less than 4 hours a hypothermia risk for
some individuals. Exposures beyond 4 h would involve increasing
probability of rapid decline into hypothermia, associated with
exhaustion of shivering and exercise heat production.
Received 12 December 1995; accepted in final form 7 March 1996.
APS Manuscript Number A1303-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96